46 



and a considerable retarding action of 

 the armature, causing it to lag so that 

 the induced electromotive force will 

 immediately be shifted back to a position 

 on the right of Oy, and, finally, as the 

 engine is supposed to give all the power 

 required for running light, equilibrium 

 will be attained by the induced electro- 

 motive force occupying a vertical posi- 

 tion, when no work is being done by the 

 current. The question now is, what 

 must be the induced electromotive force 

 to limit the current to the value of OA. ? 

 This is easily found by describing round 

 A as center with radius E„ a circle, and 

 marking its point of intersection E' with 

 the vertical Of/. That strength of field 

 which will give the induced electromotive 

 force OE' is the least which may safely 

 be permitted. The terminal electro- 

 motive force will then occupy the posi- 

 tion OE',, which line is parallel with and 

 equal to E'A. It should be observed 

 that there is between the terminal elec- 

 tromotive force and the current a differ- 

 ence of phase, amounting to nearly a 



